Various methods for obtaining a positive dye image by a heat development diffusion transfer process have been proposed. For example, JP-A-59-165054 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") discloses a method in which a dye developing agent is used and a positive dye image is formed by wet development or heat development.
JP-A-59-152440 discloses a method in which a positive dye image is formed by a heat development process using a reducible non-diffusible dye providing substance which releases a mobile dye under alkaline conditions and/or heating, but no longer releases any dye when it is reacted with exposed silver halide.
European Patent No. 220,746A2 discloses a method in which a positive dye image is formed by a heat development process using a non-diffusible dye providing substance which releases a mobile dye when it is reduced by a reducing substance (electron donor and/or electron transfer agent).
However, the above-described known positive dye image forming methods provide an inferior image in that there can be obtained only a positive dye image having low density and high stain.